The present invention relates to a bidirectional optical transmission device which is applied to an optical transceiver and optical mini-jack, and which is particularly suitable for short-distance transmission.
An optical fiber has advantages such as being small in diameter, light in weight, that is the specific gravity of glass is about one fourth of that of copper, superior in flexibility, that is, the radius of curvature is less then several centimeters, having high resistances against electromagnetic induction and crosstalk, small loss of about 1 dB/km for example, being capable of broad-band transmission, and having small problem with regard to resources. Thus optical fiber cable transmission system is widely used not only in public transmission field such as wide area network (WAN), but also in transmission system called local area network (LAN), and data bus, data link and various measurement and control systems.
Moreover, in a personal area network (PAN), there has been used an optical transmission module having a single optical fiber cable, the diameter of which is about 1 mm, connected to a light-emitting device and a light receiving device provided in a housing. The optical transmission module is adapted for optical transceiver for unidirectional transmission. Moreover, two sets of the unilateral optical transmission modules are assembled to form a double-core bidirectional optical transmission module. However, there has not been proposed a bidirectional optical transmission device having a single core which can be adapted to a compact bidirectional optical transmission module.
An example of the conventional double-core bidirectional optical transmission module is described hereinafter with reference to FIG. 6 showing a sectional view thereof.
Referring to FIG. 6, a double-core bidirectional optical transmission module (jack) 80 comprises a housing 81 having a horizontal partition 82, thereby dividing the housing 81 into a lower portion and an upper portion. In the lower portion, there is provided a light-emitting device 83 and a light-receiving device 84.
The light-emitting device 83 comprises a substrate 85a mounted on the bottom of the housing 81, an IC 86 mounted on the substrate 85a for converting an electric signal of a logic level into a light-emitting element driving signal, and a light-emitting element 87 mounted on the substrate 85a and comprising an LED for converting the driving signal to an optical signal. The IC 86 and the light-emitting element 87 are sealed by a transparent resin 88.
The light-receiving device 84 comprises a substrate 85b mounted on the bottom of the housing 81 and light-receiving IC 89 mounted on the substrate 85b, integrally incorporating a photodiode for converting an optical signal into an electric signal, and an IC for amplifying the electric signal to a logic level. The light-receiving IC 89 is also sealed by the transparent resin 88.
The substrates 85a and 85b are connected to terminals (not shown) formed on the outer wall of the housing 81 so as to be connected to external devices.
For the bidirectional optical transmission module 80, there is provided a bidirectional optical transmission double-core fiber cable 71. The fiber cable 71 comprises an optical fiber 71a for receiving light, an optical fiber 71b for emitting light, and a plug 71c for binding the optical fibers 71a and 71b together. The plug 71c is inserted in the housing 81, and each of the optical fibers 71a and 71b is inserted in an opening formed in the partition 82 so as to oppose an end thereof against the light-receiving device 84 or the light-emitting device 83.
In operation, an optical signal fed through the optical fiber 71a is applied to the light-receiving IC 89 through the transparent resin 88, whereby the signal is converted into an electric signal. On the other hand, electric signal fed to the light-emitting element 87 is converted into an optical signal and enters the optical fiber 71b through the transparent resin 88 so as to be externally transmitted.
However, the conventional bidirectional optical transmission module requires the optical fiber cable having two cores. Moreover, it is necessary to take precautions when assembling the optical fiber cable and the optical transmission module so as not to confuse the input and the output thereof. In addition, the double-core optical fiber cable is more rigid than a single-core optical fiber cable and therefore less flexible. Furthermore, the conventional bidirectional optical transmission module has separate light-emitting device and light-receiving device so that the size of the module cannot be rendered small.